1. Field of the Invention
The invention relates to a wire-type screw thread insert for insertion into a tapped hole of a workpiece consisting of a cylindrical body comprising a plurality of helically wound coils and an end coil which extends radially inwardly from the outer diameter of the cylindrical body and a use of such a wire-type screw insert in a tapped hole of a workpiece.
2. Description of the Related Art
Such wire-type screw thread inserts have become known, e.g. from U.S. Pat. No. 2,363,789, EP-A-140 812 and EP-A-157 715. Generally, the outer diameter of the cylindrical body is to be designed so as to exceed the outer diameter of the tapped hole in the workpiece so that the diameter of the wire coils is to be reduced when the insert is threaded into the tapped hole of the workpiece in order to provide for a tight grip of the screw thread coils in the tapped hole by resilient deformation of the wire coils. In order to facilitate threading of the wire-type screw thread insert into the tapped hole, half a coil at the end of the cylindrical body is deformed radially inwards in a manner known per se (EP-B1-0 228 981). The minimal outer diameter of the radially deformed portion should be substantially as large as or slightly larger than the associated outer diameter of the tapped hole. Furthermore, with this prior art wire-type screw thread insert the cross-section of the wire at the end thereof is reduced in a predetermined manner in order to facilitate insertion thereof and to avoid damaging the tapped hole. According to U.S. Pat. No. 2,152,681 the outer diameter of the reduced end portion is somewhat smaller than the outer diameter of the tapped hole. The circumferential angle of the reduced diameter portion again is 180.degree.. A similar wire-type screw thread insert has become known from U.S. Pat. No. 2,371,674 wherein, as may be seen in FIGS. 1 and 2 of that document, the end coil extends, following its diameter reducing portion, through a small angular range about a circumferential angle of somewhat more than 180.degree..